PLEASE HELP!!! Over rev problem (On a 90 Mustang GT)

OK... I've owned a 90 Mustang GT for about a year now, and about
halfway though my
ownership i've noticed a irritating problem where the car has a
tendancy to rev even when I'm off the accelerator! It's an on and off
problem which makes it especially anoying because sometimes I can drive
the car for an hour with no problem but it might occur if I start it
the next day and will continue. Ussually I know the problem is
occuring after I start the car and the idle switches to a lift reving
without any involvement from me (like, maybe from idle up to 1500rpm's
or so-over and over again). But I have had it go up to over 2000rpm's
and stay there while I was at a stop light. Most commonly though, it
sometimes revs while i'm shifting which makes smooth shifts nearly
impossible and I know it's not very good for the transmission.
The car has all the common bolt-ons: shorty headers, Flowmasters,
underdrive pulleys, k and n filter. But I think the problem might
have something to do with the aftermarket MAF meter, which is a 76mm C
and L. I haven't done any mods to the car while owning it that might
have thrown someting off.

But what should I do? Any good advice would be really appreciated!

"5.0 Mustang luver" > wrote in message
oups.com...
> OK... I've owned a 90 Mustang GT for about a year now, and about
> halfway though my
> ownership i've noticed a irritating problem where the car has a
> tendancy to rev even when I'm off the accelerator! It's an on and off
> problem which makes it especially anoying because sometimes I can drive
> the car for an hour with no problem but it might occur if I start it
> the next day and will continue. Ussually I know the problem is
> occuring after I start the car and the idle switches to a lift reving
> without any involvement from me (like, maybe from idle up to 1500rpm's
> or so-over and over again). But I have had it go up to over 2000rpm's
> and stay there while I was at a stop light. Most commonly though, it
> sometimes revs while i'm shifting which makes smooth shifts nearly
> impossible and I know it's not very good for the transmission.
> The car has all the common bolt-ons: shorty headers, Flowmasters,
> underdrive pulleys, k and n filter. But I think the problem might
> have something to do with the aftermarket MAF meter, which is a 76mm C
> and L. I haven't done any mods to the car while owning it that might
> have thrown someting off.
>
> But what should I do? Any good advice would be really appreciated!
>

there is the air bypass valve you can clean (It is bolted on the right
side(front of car) of the trhottlebody, leaks air in for idle)
It has a plunger in it and crankcase air goes through it gumming it up,
(usally sticks closed, stalls at stops)
check to see if the throttle cable is sticking and holding throttle plate
open.
clean plate and area.
sounds like it always wants to idle high
Carb spray, manyal says do not use carb spary ,but I use carb spray, work
ok, they gonna get me someday.

by for now 5.0 93 with a 8# keene-bell

I had a 5.0 HO 93 T-bird that I bought with an idle of 1800 RPM, lets just
say going 50 mph you didn't need to touch the go pedal! Took it to a Ford
dealership and they replaced the O2 sensor, throttle position sensor (or
was it called the RPM sensor?), and I don't think they touched the MAF
sensor. Bill came out to around $550 (ya, I would have saved some money at
an independant shop), but the motor ran like a dream after. Later learned
from the previous owner that he had the motor rebuilt and broke a "few"
sensors. Still, I had a HO T-bird that no rice burner could touch for $1500.
Not too shabby.

Hope this helps.

Hrvoje


"5.0 Mustang luver" > wrote in message
oups.com...
> OK... I've owned a 90 Mustang GT for about a year now, and about
> halfway though my
> ownership i've noticed a irritating problem where the car has a
> tendancy to rev even when I'm off the accelerator! It's an on and off
> problem which makes it especially anoying because sometimes I can drive
> the car for an hour with no problem but it might occur if I start it
> the next day and will continue. Ussually I know the problem is
> occuring after I start the car and the idle switches to a lift reving
> without any involvement from me (like, maybe from idle up to 1500rpm's
> or so-over and over again). But I have had it go up to over 2000rpm's
> and stay there while I was at a stop light. Most commonly though, it
> sometimes revs while i'm shifting which makes smooth shifts nearly
> impossible and I know it's not very good for the transmission.
> The car has all the common bolt-ons: shorty headers, Flowmasters,
> underdrive pulleys, k and n filter. But I think the problem might
> have something to do with the aftermarket MAF meter, which is a 76mm C
> and L. I haven't done any mods to the car while owning it that might
> have thrown someting off.
>
> But what should I do? Any good advice would be really appreciated!
>

5.0 Mustang luver wrote:
> OK... I've owned a 90 Mustang GT for about a year now, and about
> halfway though my
> ownership i've noticed a irritating problem where the car has a
> tendancy to rev even when I'm off the accelerator! It's an on and off
> problem which makes it especially anoying because sometimes I can drive
> the car for an hour with no problem but it might occur if I start it
> the next day and will continue. Ussually I know the problem is
> occuring after I start the car and the idle switches to a lift reving
> without any involvement from me (like, maybe from idle up to 1500rpm's
> or so-over and over again). But I have had it go up to over 2000rpm's
> and stay there while I was at a stop light. Most commonly though, it
> sometimes revs while i'm shifting which makes smooth shifts nearly
> impossible and I know it's not very good for the transmission.
> The car has all the common bolt-ons: shorty headers, Flowmasters,
> underdrive pulleys, k and n filter. But I think the problem might
> have something to do with the aftermarket MAF meter, which is a 76mm C
> and L. I haven't done any mods to the car while owning it that might
> have thrown someting off.
>
> But what should I do? Any good advice would be really appreciated!


Mine did the EXACT same thing. Cleaning the IAC cleared it up 100%.
Here's a site that describes the procedure with pictures:

http://www.muscularmustangs.com/iac.php

Good luck,
John
93 GT (now with 3.55s)

Sound like Throttle Position Sensor. About $25 bucks and 5 minutes.


"5.0 Mustang luver" > wrote in message
oups.com...
> OK... I've owned a 90 Mustang GT for about a year now, and about
> halfway though my
> ownership i've noticed a irritating problem where the car has a
> tendancy to rev even when I'm off the accelerator! It's an on and off
> problem which makes it especially anoying because sometimes I can drive
> the car for an hour with no problem but it might occur if I start it
> the next day and will continue. Ussually I know the problem is
> occuring after I start the car and the idle switches to a lift reving
> without any involvement from me (like, maybe from idle up to 1500rpm's
> or so-over and over again). But I have had it go up to over 2000rpm's
> and stay there while I was at a stop light. Most commonly though, it
> sometimes revs while i'm shifting which makes smooth shifts nearly
> impossible and I know it's not very good for the transmission.
> The car has all the common bolt-ons: shorty headers, Flowmasters,
> underdrive pulleys, k and n filter. But I think the problem might
> have something to do with the aftermarket MAF meter, which is a 76mm C
> and L. I haven't done any mods to the car while owning it that might
> have thrown someting off.
>
> But what should I do? Any good advice would be really appreciated!
>
>